JPH0729765B2 - Iron carbide fine particles and method for producing the same - Google Patents

Description

The present invention relates to iron carbide fine particles and a method for producing the same.

(Prior Art) Needle-like iron oxyhydroxide or needle-like iron oxide is replaced with CO or H ₂
It is known that iron particles containing iron carbide are produced by contacting with a mixture of and at 250 to 400 ° C., and they are chemically stable, have high coercive force, and are useful as a magnetic material for a magnetic recording medium. (For example, JP-A-60-71509,
60-108309, 60-127212, 60-155522). Since iron carbide fine particles are generally used as a coating type magnetic recording medium, pigment characteristics are also required. However, since reduction or carbonization treatment may cause sintering or deformation of the shape, the reduction or carbonization treatment is generally performed by depositing a silicon or aluminum compound on the surface of the raw material. However, although the sintering and the collapse of the shape are prevented, the free carbon is remarkably deposited on the produced particles, which causes a problem such as deterioration of magnetic properties.

(Problems to be Solved by the Invention) An object of the present invention is to provide iron carbide fine particles which are excellent in magnetic properties without sintering and shape deterioration, and a method for producing the same.

(Means for Solving the Problem) The present invention relates to iron carbide fine particles containing Fe ₅ C ₂ as a main component, which are obtained by depositing a nickel compound and further depositing a silicon compound and an aluminum compound. For example, (a) after adding an aqueous solution of a nickel compound, a neutralization reaction is performed, and after adding an aqueous solution of a silicon compound and an aluminum compound, the neutralization reaction is carried out, and iron oxyhydroxide or iron oxide fine particles contain carbon. It can be obtained by contacting (b) a carbon-containing reduced carbonizing agent or a mixture of the carbon-containing reducing agent and a reducing carbon-containing reducing agent after or without contacting the non-reducing agent.

In the iron carbide fine particles of the present invention, the deposition amount of the nickel compound and the deposition amount of the silicon compound and the aluminum compound are each 0.01 in terms of element with respect to the Fe ₂ O ₃ equivalent weight of iron.
It is preferably ˜10 wt%. Here, the element means an element selected from the group of nickel, silicon and aluminum.

In the production method of the present invention, iron oxyhydroxide is α-FeOO
H (goethite), β-FeOOH (akaganesite) or γ
-FeOOH (lepidocrocite) is preferable, and iron oxide is
α-Fe ₂ O ₃ (hematite), γ-Fe ₂ O ₃ (maghemite)
Alternatively, Fe ₃ O ₄ (magnetite) is preferable.

Examples of the above α-Fe ₂ O ₃ or γ-Fe ₂ O ₃ include α-Fe ₂ O ₃
OOH, β-FeOOH or γ-FeOOH about 200-350 ℃
Obtained by heating and dehydrating to 0 ° C, or α-Fe which has been further densified by heating these to about 350-900 ℃
Any of ₂ O ₃ , γ-Fe ₂ O _3, etc. can be used. β-FeOO
H is preferably treated with an alkaline aqueous solution.

The above-mentioned Fe ₃ O ₄ is produced by contacting iron oxide or iron oxyhydroxide other than Fe ₃ O ₄ with a reducing carbonizing agent containing carbon, a reducing agent containing no carbon, or a mixture thereof. You can Of course, the above-mentioned Fe ₃ O ₄ is not limited to that produced by this production method. As a special case, when preparing the mixture is contacted with an iron oxide other than iron oxyhydroxide or Fe ₃ O ₄ Fe ₃ O ₄ with a reducing agent containing no reducing carbonization agent or its carbon containing carbon As compared with the contact condition of the step (b) in the present invention described later, the contact condition can be the same except for the time. In that case, after the production of Fe ₃ O ₄ , contact can be continued under the same conditions to produce the intended particles of the present invention.

In the present invention, iron oxyhydroxide or iron oxide having an average axial ratio of 3 or more, particularly 3 to 20 is suitable, and the average particle size (major axis) is usually 2 μm or less, preferably 0.1 to 2 μm, and most preferably. Is 0.1 to 1.0 μm. As will be described later, the particles produced have an average axial ratio and an average particle diameter which are slightly smaller than those of these raw materials but hardly change. This is because it is suitable.

Further, iron oxyhydroxide or iron oxide used in the present invention,
As long as the main component is iron oxyhydroxide or iron oxide, a small amount of copper, magnesium, manganese, nickel, cobalt oxides, carbonates; silicon oxides; potassium salts, sodium salts, etc. are added. You can buy it.

The above-mentioned acicular iron oxyhydroxide is preferable as described in JP-A-60-108309, and iron oxide is preferable because the particles having a higher coercive force can be obtained when the surface pH is 5 or more. pH
When the value is less than 5, the pH is preferably adjusted to 5 or more by contacting with an alkaline (eg sodium hydroxide, potassium hydroxide, ammonium hydroxide) aqueous solution. Alkaline treatment
For example, the treated material is sodium hydroxide, potassium hydroxide,
It can be carried out by contacting with an aqueous solution of an alkali such as ammonium hydroxide (for example, pH 8 or more, preferably 10 or more), stirring if necessary for 30 minutes to 1 hour, filtering and drying. .

In the present invention, the surface pH is 5 g of a sample boiled in 100 cc of distilled water for 1 hour, cooled to room temperature, and allowed to stand for 1 hour.
pH is defined as the value measured with a pH meter.

In the production method of the present invention, a film made of a nickel compound is formed on the surface of the iron oxyhydroxide or iron oxide (both may be referred to as iron compounds hereinafter), and then a film made of a silicon compound and an aluminum compound is formed. To use.

Examples of the nickel compound include nickel chloride, nickel nitrate, nickel sulfate, nickel bromide, nickel acetate and the like.

Further, examples of the silicon compound include sodium orthosilicate, sodium metasilicate, potassium metasilicate, water glass of various compositions, and the like, and examples of the aluminum compound include aluminum sulfate, aluminum nitrate, aluminum chloride, various aluminum alum, sodium aluminate, and aluminum. Examples thereof include potassium acid.

The deposition of these metal compounds on the surface of the iron compound is carried out, for example, by adding an aqueous solution of the metal compound to a suspension of the iron compound and then conducting a neutralization reaction. Incidentally, after the neutralization reaction in the first deposition step, there is no particular need for excess and drying, but after the neutralization reaction in the second deposition step, there is a need for excess and drying. The amount of these metal compounds deposited is Fe ₂ O of iron oxyhydroxide or iron oxide.
_It is preferably 0.01 to 10 wt% in terms of element with respect to ₃ equivalent weight. Next, the iron compound fine particles obtained above are subjected to a catalytic reaction.

Typical examples of the carbon-free reducing agent in the production method of the present invention include H ₂ and NH ₂ NH ₂ .

As the carbonizing agent containing carbon, at least one of the following compounds can be used.

CO 2 aliphatic, linear or cyclic, saturated or unsaturated hydrocarbons such as methane, propane, butane, cyclohexane, methylcyclohexane, acetylene, ethylene, propylene, butadiene, isoprene, town gas and the like.

Aromatic hydrocarbons such as benzene, toluene, xylene, and their alkyl and alkenyl derivatives having a boiling point of 150 ° C or lower.

Aliphatic alcohols such as methanol, ethanol, propanol, cyclohexanol.

Boiling point of esters such as methyl formate and ethyl acetate
Ester below 150 ℃.

Ethers such as lower alkyl ethers and vinyl ethers having a boiling point of 150 ° C or lower.

Aldehydes such as formaldehyde and acetaldehyde having a boiling point of 150 ° C or lower.

Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, etc., having a boiling point of 150 ° C. or less.

Particularly preferred carbon-containing reducing carbonizing agents are CO, CH ₃ OH, H
COOCH _{3 is} a saturated or unsaturated aliphatic hydrocarbon having 1 to 5 carbon atoms.

In the step (a) of the present invention, the carbon-free reducing agent can be used with or without dilution, and examples of the diluent include N ₂ , CO ₂ , argon, helium and the like. . Although the dilution ratio can be selected arbitrarily,
It is preferable to stop the dilution up to 10 times (volume ratio). The contact conditions such as contact temperature, contact time, and flow rate vary depending on, for example, the production history of the iron compound, the average axial ratio, the average particle size, the specific surface area, and the like, and thus may be appropriately selected. The preferred contact temperature is about 200-700 ° C, more preferably about 300-400 ° C, and the preferred contact time is about 0.5-6 hours. A preferred flow rate is about 1-1000 ml STP / min / g of raw iron compound. The contact pressure is usually 1 to 2 atm including the diluent, but is not particularly limited.

Also in the step (b) of the production method of the present invention, the reducing carbonizing agent containing carbon or a mixture of the reducing carbonizing agent and the reducing agent not containing carbon can be used with or without dilution. When a mixture is used, its mixing ratio can be appropriately selected, but normally, it is preferable that the volume ratio of the reducing carbonizing agent containing carbon and the reducing agent not containing carbon be up to 1/5. The contact conditions can be similarly appropriately selected, but the preferred contact temperature is about 250 to 400 ° C, more preferably about 300.
~ 400 ° C, the preferable contact time is about 0.5 to 6 hours when the step (a) is carried out, and about 1 to 12 when the step (a) is not carried out.
It's time. A preferred flow rate is about 1-1000 ml STP / min / g of raw iron compound. The contact pressure is usually 1 to 2 atm including the diluent, but is not particularly limited.

The particles obtained in the present invention, when observed by an electron microscope, are uniformly particles having the same shape as the particles of the raw material iron oxide, and these skeleton particles are present as primary particles. ing. Further, it is clear that the obtained particles contain carbon by elemental analysis and further contain iron carbide by X-ray diffraction pattern. The X-ray diffraction pattern shows interplanar spacings of 2.28, 2.20, 2.08, 2.05 and 1.92Å. Such a pattern corresponds to Fe ₅ C ₂ , and the iron carbide of the present invention usually consists mainly of Fe ₅ C ₂ , but Fe ₂ C, Fe ₂₀ C ₉ (Fe
_2.2 C), Fe ₃ C, etc. may coexist. Therefore, the iron carbide contained in the particles of the present invention is appropriately represented by FexC (2 ≦ x <3).

The iron carbide fine particles of the present invention can be used as a magnetic material for magnetic recording, as is apparent from the above-mentioned characteristics, but the present invention is not limited to this, and the lower aliphatic hydrocarbons CO and H ₂ can be used. It can also be used as a catalyst or the like for synthesis.

(Effects of the Invention) According to the method of the present invention, it is possible to produce iron carbide fine particles that are free from sintering and shape deterioration, have excellent magnetic properties, and have a small amount of precipitated carbon.

(Example) Below, a reference example, an Example, and a comparative example are given and demonstrated in detail.

In the examples, various characteristics were obtained by the following methods.

(1) Magnetic properties Unless otherwise specified, it is determined by the following method.

Sample filling rate of 0 with a Gauss meter using a Hall element.
At 2, the coercive force (Hc, Oe), the saturation magnetization (σs, emu / g), and the squareness ratio (Sq) are measured with a measurement magnetic field of 5 kOe.

(2) Elemental analysis of C, H and N Elemental analysis is MT2 CHN CORDER Yanac manufactured by Yanagimoto Manufacturing Co., Ltd.
O is used and oxygen (helium carrier) is passed at 900 ° C according to a conventional method.

Reference Example 1 8 g of goethite particles having an average particle size of 0.5 μm and an average axial ratio of 12 (Fe ₂
7.2 g of O ₃ was suspended in 0.5 l of pure water. Next, adjust the pH to 5 with 1N-HCl aqueous solution, add a predetermined amount of the metal compound to be adhered to the predetermined destination shown in Table 1, stir, and then add pH to 1N-NaOH.
The metal compound was deposited by adjusting to 9.0. Then 1N-Na
The pH was adjusted to 10 with OH, and a predetermined amount of the compound to be further adhered as shown in Table 1 was added and stirred, and the pH was adjusted with 0.5N-HCl aqueous solution.
Adjusted to 7.0 and applied the compound. Next, this was washed with water, dried and dried to obtain goethite particles to which the metal compound to be previously deposited and the compound to be further deposited were deposited.

Reference Example 2 The goethite particles obtained in Reference Example 1 were heated in air at 500 ° C for 3
Α-Fe ₂ O coated with the previously deposited metal compounds and further deposited compounds described in Table 1 after heating for 0 minutes and dehydration
Got _three .

Example 1 2 g of α-Fe ₂ O ₃ particles obtained in Reference Example 1 was added with CO at 500 m / min at 380 ° C.
The powder was contacted at a flow rate of 1 for 3 hours and then left to cool to room temperature to obtain a black powder. The X-ray diffraction pattern of the product is ASTM X-
Ray Powder Data File Matched with 20-509 Fe ₅ C ₂ Iron Carbide. The magnetic properties are shown in Table 2.

Comparative Example 1 A black powder was obtained in the same manner as in Example 1 except that the deposition of the nickel compound and the silicon compound was omitted.

Comparative Example 2 A black powder was obtained in the same manner as in Example 1, except that the deposition of the silicon compound and the aluminum compound was omitted.

Claims (3)

[Claims] 1. Iron carbide fine particles containing Fe ₅ C ₂ as a main component, which are obtained by depositing a nickel compound and further depositing a silicon compound and an aluminum compound. 2. The iron carbide according to claim 1, wherein the amount of nickel compound deposited and the amount of silicon compound and aluminum compound deposited are each 0.01 to 10 wt% in terms of element relative to the Fe ₂ O ₃ equivalent weight of iron. Fine particles. 3. After adding (a) an aqueous solution of a nickel compound,
After a neutralization reaction and further addition of an aqueous solution of a silicon compound and an aluminum compound, after contacting a reducing agent containing no carbon with the iron oxyhydroxide or iron oxide fine particles obtained by the neutralization reaction, or without contact. (B) A method for producing iron carbide fine particles containing Fe ₅ C ₂ as a main component, which comprises contacting a reducing carbonizing agent containing carbon or a mixture of the reducing carbonizing agent and a reducing agent containing no carbon.